[lldb] Fix 'error: non-const lvalue...' caused by SWIG 4.1.0

Fix the failure caused by change in SwigValueWraper for C++11 and later
for improved move semantics in SWIG commit.

swig/swig@d1055f4
(cherry picked from commit f0a25fe)

lldb/bindings/python/python-typemaps.swig

@@ -435,7 +435,7 @@ template <> bool SetNumberFromPyObject<double>(double &number, PyObject *obj) {
 
 %typemap(out) lldb::FileSP {
   $result = nullptr;
-  lldb::FileSP &sp = $1;
+  const lldb::FileSP &sp = $1;
   if (sp) {
     PythonFile pyfile = unwrapOrSetPythonException(PythonFile::FromFile(*sp));
     if (!pyfile.IsValid())